1. Field of the Invention
The present invention relates to an improvement in a document size-detecting device detecting the size of the document placed on a platen for a copying machine such as an electrophotographic copying machine and others.
2. Description of the Prior Art
Heretofore, Japanese Patent Publication Open to Public Inspection No: 11242/1975 has shown a copying machine wherein copy papers in different sizes or papers in roll type are loaded and a sheet of paper with a suitable size for the size of a document placed on a platen of the copying machine is selected or cut and then conveyed. In the document size-detecting device of such copying machine, the light projecting devices and the photoelectric converting devices are provided in parallel along the diagonal direction of the document on both the document-holding cover (platen cover) and the under surface of the platen so that the light projecting device and the photoelectric converting device oppose each other and the detection of the document size is made based on the information of the sizes of output of the photoelectric converting devices in parallel. On such a document size-detecting device, owing to the dispersion of the sensitivity of photoelectric converting devices in parallel, the dispersion and variation of the emission intensity of the light projecting device and further to the external light that enters leaking through the clearance of the platen cover, it is feared that the information on the size of output of the photoelectric converting device does not necessarily reflect the size of the document and thereby it causes an erroneous selection of the paper. Further, either one of light projecting device and photoelectric converting device is provided on the platen cover that is opened and closed, therefore a failure tends to take place thereon and the shade of the light projecting device or of the photoelectric converting device appears on the copy paper, which is disadvantageous.
The present applicant has made a proposal in Japanese Patent Publication Open to Public Inspection No. 22424/1981 (U.S. application Ser. No. is 172,821/1980) with an object to provide the document size-detecting device that solves aforesaid problems. The proposal includes a document size-detecting device for the copying machine comprising a colored portion that is colored to a certain color, the light projecting device irradiating the colored portion and the light-receiving member that receives the light irradiated from the light projecting device and is reflected on the colored portion, and is characterized in that a part of or all of the light irradiated from aforesaid light projecting device to aforesaid light-receiving member are intercepted by the document placed on the platen and thereby the size of the document is detected.
Namely, in the document size-detecting device of aforesaid proposal, the characteristics of the light-receiving member where plurality of the detecting elements capable of obtaining signals proportional to the wavelength of incident light are arranged, are utilized thereby the reflected light or the transmitted light from the colored portion which is not covered by the document is detected and the detection of document size is made according to the information relating to the existence of aforesaid detection made by detecting elements in parallel relating to document size.
Aforesaid proposal has advantages that there is no dispersion of sensitivity which has been experienced in the light-receiving member of the conventional photoelectric converting device and that it is hardly influenced by the dispersion variation of radiation intensity of the light projecting device and by the external light whose intensity ratio for the specific wavelength relating to the colored portion is low and thereby there is not a fear of erroneous operation. On the other hand, however, the document size-detecting device of aforesaid proposal has detecting elements for each document size to be detected and detection of document size is made by the combination of outputs of the detecting elements. Therefore it is necessary to use a lot of detecting elements and function thereof is complicated, then inexpensive document size-detecting device has not been available. Further, when the color of the document is similar to or close to the color of colored portion, the detecting capability may fall, which has been a disadvantage.